Orthodontics is a branch of dentistry that involves the movement of malpositioned teeth to orthodontically correct positions. Before prescribing an orthodontic treatment, X-rays and photographs of the patient's teeth and jaw structure are typically taken. Also, a mold of the patient's teeth is typically made. This mold, along with the X-rays and photographs, provide a model of the positions of the patient's teeth and dental arches prior to treatment.
The orthodontist also relies on a post treatment model of the altered positions of the patient's teeth and dental arches. This post-treatment model has typically been a mental model formulated in the mind of the orthodontist based on the orthodontist's experience and skill. However, computer programs are also known to assist the orthodontist in the development of a computerized post-treatment model. The orthodontist then devises an initial treatment strategy to move the patient's teeth and/or dental arches from their positions as represented by the pre-treatment model to the altered positions as represented by the post-treatment model, sometimes using interim steps to arrive at the ultimate position.
In order to implement the initial treatment strategy, the orthodontist applies various orthodontic appliances to the patient's teeth. In a typical treatment, brackets are attached to anterior, cuspid, bicuspid, and molar teeth. An arch wire is then held to the brackets by ligatures, so that the arch wire forms a track to guide movement of the brackets and the associated teeth to desired positions for correct occlusion. The brackets, arch wires, ligatures, and other ancillary devices used in correctly positioning teeth are commonly referred to as “braces”.
The orthodontist's treatment strategy may require correction of the relative alignment between the upper and lower dental arches. For example, certain patients have a condition referred to as a Class II malocclusion in which the lower dental arch is located an excessive distance in a rearward direction relative to the location of the upper dental arch when the jaws are closed. Other patients may have an opposite condition referred to as a Class III malocclusion in which the lower dental arch is located in a forward direction of its desired location relative to the position of the upper dental arch when the jaws are closed.
Orthodontic treatment of Class II and Class III malocclusions are commonly corrected by movement of the upper and lower dental arches as units relative to one another. To this end, forces are often applied to each dental arch as a unit by applying a force to the brackets, the arch wires, and/or ancillary devices applied to the dental arch. In this manner, a Class II or Class III malocclusion can be corrected at the same time that the arch wires and the brackets are used to move individual teeth to desired positions relative to each other.
Corrections of Class II and Class III malocclusions are sometimes carried out by use of other devices such as headgear that includes strapping extending around the rear of the patient's head. The strapping is often coupled by tension springs to the brackets, arch wires, and/or ancillary devices. For correction of Class III malocclusions, the strapping can be connected by tension springs to a chin cup that externally engages the patient's chin. In either instance, the strapping and springs serve to apply a rearward force to the associated jaw.
Instead of using headgear, which is often considered unsatisfactory because it is visibly apparent, many practitioners and patients favour the use of intra-oral devices for correcting Class II and Class III malocclusions. Such devices are often located near the cuspid, bicuspid, and molar teeth and away from the patient's anterior teeth. As a result, intra-oral devices for correcting Class II and Class III malocclusions are hidden in substantial part once installed.
Orthodontic force modules made of an elastomeric material have also been used to treat Class II and Class III malocclusions. Pairs of such force modules are coupled between the dental arches on opposite sides of the oral cavity. Elastomeric force modules may be used in tension to pull the jaws together in a direction along reference lines that extend between the points of attachment of each force module. Such force modules may be O-rings or chain-type modules each made of a number of integrally connected O-rings. These modules are typically removable by the patient for replacement when necessary, since the module may break or the elastomeric material may degrade during use to such an extent that the amount of tension exerted is not sufficient. Non-removable intra-oral devices are also known which rely on flexible members that are connected to upper and lower dental arches of a patient. Moreover, telescoping tube assemblies may be used to urge the dental arches toward positions of improved alignment.
There are a wide variety of orthodontic appliances that are available to an orthodontist in the implementation of a treatment strategy. However, few tools exist to assist the orthodontist in the accurate selection of appliances that are likely to effectively implement the orthodontist's initial treatment strategy. Moreover, few tools exist to allow the orthodontist to accurately predict the effectiveness of the initial treatment strategy. Therefore, the treatment strategy is frequently modified over time as the orthodontist observes the actual movement of the teeth and dental arches in response to the orthodontist's treatment strategy.